1. Field of the Invention
The invention relates to a high-temperature protection layer.
2. Brief Description of the Related Art
High-temperature protection layers of this type are used in particular where the base material of components made from heat-resistant steels and/or alloys used at temperatures over 600° C. is to be protected.
These high-temperature protection layers are intended to slow down or completely suppress the action of high-temperature corrosion, in particular caused by sulfur, oil ashes, oxygen, alkaline-earth metals and vanadium. High-temperature protection layers of this type are formed in such a way that they can be applied direct to the base material of the component that is to be protected.
High-temperature protection layers are of particular importance for components of gas turbines. They are applied in particular to rotor blades and guide vanes and to heat-accumulation segments of gas turbines.
It is preferable to use an austenitic material based on nickel, cobalt or iron to produce these components. In particular nickel superalloys are used as base material in the production of gas turbine components.
Hitherto, it has been customary to provide components intended for gas turbines with protection layers which are formed by alloys whose main constituents are nickel, chromium, aluminum and yttrium. High-temperature protection layers of this type have a matrix in which an aluminum-containing phase is embedded.
Most of the coatings used for high-temperature applications originate from the NiCrAlY, CoCrAlY or NiCoCrAlY families. The layers differ by virtue of the concentration of the “family members” nickel, cobalt, chromium, aluminum and yttrium and by virtue of further elements being added. The composition of the layer is the crucial factor in determining the performance at high temperatures in an oxidizing and/or corrosive atmosphere, in the event of temperature changes and under mechanical loading. Moreover, the composition of the layer determines the materials costs and production costs. Many known layers have excellent properties only for some of the aspects. Although in widespread use throughout the world, both corrosion resistance and the costs are adversely affected by the addition of cobalt, as our own investigations have determined.
Documents JP-A-53 085736, U.S. Pat. No. 3,620,693, U.S. Pat. No. 4,477,538, U.S. Pat. No. 4,537,744, U.S. Pat. No. 3,754,903, U.S. Pat. No. 4,013,424, U.S. Pat. No. 4,022,587 and U.S. Pat. No. 4,743,514 have disclosed numerous alloys belonging to the “cobalt-free NiCrAlY family”. Thermodynamic modeling of the phase composition of these alloys for the temperature range from 800° C. to 1050° C. has shown that the specified compositions lead to microstructures with undesirable phases or thermally activated phase transitions, specifically σ-and/or β-NiAl, in disadvantageously high proportions by volume.